Optical processing

• US 20050018259A1
• Filed: 09/02/2002
• Published: 01/27/2005
• Est. Priority Date: 09/03/2001
• Status: Active Grant

• Current Assignee: Thomas Swan & Company Limited (Aixtron AG)
• Original Assignee: Thomas Swan & Company Limited (Aixtron AG)
• Inventors: Holmes, Melanie
• Granted Patent: US 7,145,710 B2
• Time in Patent Office: Days
• US Class Current: 359/3
• CPC Class Codes: G02B 26/06 for controlling the phase of light G02B26/08 takes precedence , measuring optical phase difference G01J9/00
• CPC Class Codes: G02B 26/0808 by means of one or more diffracting elements
• CPC Class Codes: G02B 26/0833 the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD G02B26/0825 takes precedence; micromechanical devices in general B81B
• CPC Class Codes: G02B 5/32 Holograms used as optical elements
• CPC Class Codes: G02B 6/266 the optical element being an attenuator
• CPC Class Codes: G02B 6/29311 Diffractive element operating in transmission
• CPC Class Codes: G02B 6/29314 by moving or modifying the diffractive element, e.g. deforming
• CPC Class Codes: G02B 6/2938 for multiplexing or demultiplexing, i.e. combining or separating wavelengths, e.g. 1xN, NxM
• CPC Class Codes: G02B 6/29391 Power equalisation of different channels, e.g. power flattening
• CPC Class Codes: G02B 6/3512 the optical element being reflective, e.g. mirror
• CPC Class Codes: G02B 6/3534 the optical element being diffractive, i.e. a grating
• CPC Class Codes: G02B 6/3548 1xN switch, i.e. one input and a selectable single output of N possible outputs
• CPC Class Codes: G02B 6/3556 NxM switch, i.e. regular arrays of switches elements of matrix type constellation
• CPC Class Codes: G02F 1/1326 Liquid crystal optical waveguides or liquid crystal cells specially adapted for gating or modulating between optical waveguides
• CPC Class Codes: G02F 1/13342 Holographic polymer dispersed liquid crystals
• CPC Class Codes: G02F 1/1335 Structural association of cells with optical devices, e.g. polarisers or reflectors
• CPC Class Codes: G02F 1/29 for the control of the position or the direction of light beams, i.e. deflection
• CPC Class Codes: G02F 1/291 Two-dimensional analogue deflection
• CPC Class Codes: G02F 1/31 Digital deflection, i.e. optical switchingG02F1/33 takes precedence
• CPC Class Codes: G02F 1/3132 of directional coupler type
• CPC Class Codes: G02F 2201/30 : grating
• CPC Class Codes: G02F 2201/34 : reflector
• CPC Class Codes: G02F 2203/12 : spatial light modulator
• CPC Class Codes: G02F 2203/28 : focussing or defocussing
• CPC Class Codes: G02F 2203/50 : Phase-only modulation
• CPC Class Codes: G03H 1/0005 : Adaptation of holography to specific applications holographic optical element G02B5/32; holographic scanner G02B26/106; recognition using holographic mask G06V10/88; holographic memories G11B7/0065, G11C13/042
• CPC Class Codes: G03H 1/02 : Details of features involved during the holographic process; Replication of holograms without interference recording
• CPC Class Codes: G03H 1/04 : Processes or apparatus for producing holograms G03H1/26 takes precedence
• CPC Class Codes: G03H 1/08 : Synthesising holograms, i.e. holograms synthesized from objects or objects from hologramsusing electric digital computers G06F; G06T
• CPC Class Codes: G03H 1/0866 : Digital holographic imaging, i.e. synthesizing holobjects from holograms
• CPC Class Codes: G03H 1/0891 : Processes or apparatus adapted to convert digital holographic data into a hologram G03H1/2294 takes precedence
• CPC Class Codes: G03H 1/2286 : Particular reconstruction light G03H1/24 takes precedence; Beam properties
• CPC Class Codes: G03H 1/2294 : Addressing the hologram to an active spatial light modulator
• CPC Class Codes: G03H 1/26 : Processes or apparatus specially adapted to produce multiple sub- holograms or to obtain images from them, e.g. multicolour technique
• CPC Class Codes: G03H 2001/0224 : Active addressable light modulator, i.e. Spatial Light Modulator [SLM] corresponding details, see subgroups of G03H2225/00
• CPC Class Codes: G03H 2001/0491 : by monitoring the hologram formation, e.g. via a feed-back loop
• CPC Class Codes: G03H 2001/261 : in optical contact
• CPC Class Codes: G03H 2001/264 : One hologram being a HOE
• CPC Class Codes: G03H 2222/13 : Multi-wavelengths wave with discontinuous wavelength ranges G03H2222/18 takes precedence
• CPC Class Codes: G03H 2222/32 : Unpolarised light
• CPC Class Codes: G03H 2223/23 : Diffractive element
• CPC Class Codes: G03H 2225/32 : Phase only
• CPC Class Codes: G03H 2225/52 : Reflective modulator
• CPC Class Codes: G03H 2225/60 : Multiple SLMs
• CPC Class Codes: G03H 2226/02 : Computing or processing means, e.g. digital signal processor [DSP]
• CPC Class Codes: H04J 14/021 : Reconfigurable arrangements, e.g. reconfigurable optical add/drop multiplexers [ROADM] or tunable optical add/drop multiplexers [TOADM]
• CPC Class Codes: H04J 14/0212 : using optical switches or wavelength selective switches [WSS]
• CPC Class Codes: H04J 14/0213 : Groups of channels or wave bands arrangements
• CPC Class Codes: H04J 14/0217 : Multi-degree architectures, e.g. having a connection degree greater than two
• CPC Class Codes: H04J 14/0219 : Modular or upgradable architectures
• CPC Class Codes: H04J 14/022 : For interconnection of WDM optical networks
• CPC Class Codes: H04J 14/08 : Time-division multiplex systems
• CPC Class Codes: H04Q 11/0005 : Switch and router aspects
• CPC Class Codes: H04Q 2011/0016 : using wavelength multiplexing or demultiplexing
• CPC Class Codes: H04Q 2011/0028 : using holograms
• CPC Class Codes: H04Q 2011/0039 : Electrical control

Abstract

To operate an optical device comprising an SLM with a two-dimensional array of controllable phase-modulating elements groups of individual phase-modulating elements are delineated, and control data selected from a store for each delineated group of phase-modulating elements. The selected control data are used to generate holograms at each group and one or both of the delineation of the groups and the selection of control data is/are varied. In this way upon illumination of the groups by light beams, light beams emergent from the groups are controllable independently of each other.

Claims

1. a method of operating an optical device comprising an SLM having a two-dimensional array of controllable phase-modulating elements, the method comprising

delineating groups of individual phase-modulating elements;

selecting, from stored control data, control data for each group of phase-modulating elements;

generating from the respective selected control data a respective hologram at each group of phase-modulating elements; and

varying the delineation of the groups and/or the selection of control data

whereby upon illumination of said groups by respective light beams, respective emergent light beams from the groups are controllable independently of each other;

3. A method of operating an optical device according to claim 1, wherein each phase modulating element is responsive to a respective applied voltage to provide a corresponding phase shift to emergent light, the method further comprising

controlling said phase-modulating elements of the spatial light modulator to provide respective actual holograms derived from the respective generated holograms, wherein the controlling step comprises:

resolving the respective generated holograms modulo 2pi.

4. A method of operating an optical device according to claim 1, comprising:

providing a discrete number of voltages available for application to each phase modulating element;

on the basis of the respective generated holograms, determining the desired level of phase modulation at a predetermined point on each phase modulating element and choosing for each phase modulating element the available voltage which corresponds most closely to the desired level.

5. A method of operating an optical device according to claim 1, comprising:

providing a discrete number of voltages available for application to each phase modulating element;

determining a subset of the available voltages which provides the best fit to the generated hologram.

6. A method of operating an optical device according to claim 1, further comprising the step of storing said control data wherein the step of storing said control data comprises calculating an initial hologram using a desired direction change of a beam of light, applying said initial hologram to a group of phase modulating elements, and correcting the initial hologram to obtain an improved result.

7. A method of operating an optical device according to claim 1, further comprising the step of providing sensors for detecting temperature change, and performing said varying step in response to the outputs of those sensors.

8. A method of operating an optical device according to claim 1, in which the SLM is integrated on a substrate and has an integrated quarter-wave plate whereby it is substantially polarisation insensitive.

9. A method of operating an optical device according to claim 1, wherein the phase-modulating elements are substantially reflective, whereby emergent beams are deflected from the specular reflection direction.

10. A method of operating an optical device according to claim 3 comprising, for at least one said group of phase-modulating elements, providing control data indicative of two holograms to be displayed by said group and generating a combined hologram before said resolving step.

2. A method of operating an optical device according to clam 1, wherein control of said light beams is selected from the group comprising:

control of direction, control of power, focussing, aberration compensation, sampling and beam shaping.

11. An optical device comprising an SLM and a control circuit, the SLM having a two-dimensional array of controllable phase-modulating elements and the control circuit having a store constructed and arranged to hold plural items of control data, the control circuit being constructed and arranged to delineate groups of individual phase-modulating elements, to select, from stored control data, control data for each group of phase-modulating elements, and to generate from the respective selected control data a respective hologram at each group of phase-modulating elements,

wherein the control circuit is further constructed and arranged to vary the delineation of the groups and/or the selection of control data,

whereby upon illumination of said groups by respective light beams, respective emergent light beams from the groups are controllable independently of each other.

12. An optical device according to claim 11, having sensor devices arranged to detect light emergent from the SLM, the control circuit being responsive to signals from the sensors to vary said delineation and/or said selection.

13. An optical device according to claim 11, having temperature responsive devices constructed and arranged to feed signals indicative of device temperature to said control circuit, whereby said delineation and/or selection is varied.

14. An optical routing device having at least first and second SLMs and a control circuit, the first SLM being disposed to receive respective light beams from an input fibre array, and the second SLM being disposed to receive emergent light from the first SLM and to provide light to an output fibre array, the first and second SLMs each having a respective two-dimensional array of controllable phase-modulating elements and the control circuit having a store constructed and arranged to hold plural items of control data, the control circuit being constructed and arranged to delineate groups of individual phase-modulating elements, to select, from stored control data, control data for each group of phase-modulating elements, and to generate from the respective selected control data a respective hologram at each group of phase-modulating elements,

wherein the control circuit is further constructed and arranged, to vary the delineation of the groups and/or the selection of control data

whereby upon illumination of said groups by respective light beams, respective emergent light beams from the groups are controllable independently of each other.

15. A device for shaping one or more light beams in which the or each light beam is incident upon a respective group of pixels of a two-dimensional SLM, and the pixels of the or each respective group are controlled so that the corresponding beams emerging from the SLM are shaped as required.

16. An optical device comprising one or more optical inputs at respective locations, a diffraction grating constructed and arranged to receive light from the or each optical input, a focussing device and a continuous array of phase modulating elements, the diffraction grating and the array of phase modulating elements being disposed in the focal plane of the focussing device whereby diverging light from a single point on the diffraction grating passes via the focussing device to form beams at the array of phase modulating elements, the device further comprising one or more optical output at respective locations spatially separate location from the or each optical input, whereby the diffraction grating is constructed and arranged to output light to the or each optical output.

17. A method of filtering light comprising applying a beam of said light to a diffraction grating whereby emerging light from the grating is angularly dispersed by wavelength, forming respective parallel beams from said emerging light by passing the emerging light to a focussing device having the grating at its focal plane, passing the respective parallel beams to an SLM at the focal plane of the focussing device, the SLM having a two-dimensional array of controllable phase-modulating elements, selectively reflecting light from different locations of said SLM and passing said reflected light to said focussing device and then to said grating.

18. A method according to claim 17 comprising delineating groups of individual phase-modulating elements to receive beams of light of differing wavelength;

selecting, from stored control data, control data for each group of phase-modulating elements;

generating from the respective selected control data a respective hologram at each group of phase-modulating elements; and

varying the delineation of the groups and/or the selection of control data.

19. An optical add/drop multiplexer having a reflective SLM having a two-dimensional array of controllable phase-modulating elements, a diffraction device and a focussing device wherein light beams from a common point on the diffraction device are mutually parallel when incident upon the SLM, and wherein the SLM displays respective holograms at locations of incidence of light to provide emergent beams whose direction deviates from the direction of specular reflection.

20. A test or monitoring device comprising an SLM having a two-dimensional array of pixels, and operable to cause incident light to emerge in a direction deviating from the specular direction, the device having light sensors at predetermined locations arranged to provide signals indicative of said emerging light.

21. A test or monitoring device according to claim 20, further comprising further sensors arranged to provide signals indicative of light emerging in the specular directions.

22. A power control device for one or more beams of light in which the or each beam is incident on respective groups of pixels of a two-dimensional SLM, and power-control holograms are applied to the respective groups so that the emergent beams have power reduced by comparison to the respective incident beams.

23. An optical routing module having at least one input and at least two outputs and operable to select between the outputs, the module comprising a two dimensional SLM having an array of pixels, with circuitry constructed and arranged to display holograms on the pixels to route beams of different frequency to respective outputs.

24. A routing device having an input and plural outputs, the input constructed and arranged to receive a light beam having plural wavelengths, the device comprising an optical device for selecting the wavelengths of the input beam to appear in the outputs, wherein each output may contain any desired set of the plural wavelengths.

25. A routing device according to claim 24, wherein the members of the desired set may be varied in use.

26. A routing device according to claim 24, wherein at least two of the outputs contain at least one common wavelength.

27. A routing device having plural input signals and an output, the output constructed and arranged to deliver a signal having plural wavelengths, the device comprising a device for combining the wavelengths from the input signals to appear in the output, wherein each input signal may contain any desired set of the plural wavelengths of the output.

28. A method of filtering light comprising spatially distributing the light by wavelength across an array of phase-modulating elements to form plural beams, delineating a group of said phase-modulating elements to be aligned with the centre frequency of a desired channel whereby the group truncates the beams according to wavelength, controlling the group to provide images of the truncated light beams incident on the group at a selected output waveguide wherein the original centres of the truncated light beams are substantially coincident with the centre of the output waveguide.